Determining the CKM Parameter Vcd from nuN Charm Production

TL;DR

This work analyzes how to extract the CKM element |V_{cd}| from νN charm production, detailing the LO and higher-order QCD framework, hadronization, and nuclear effects that influence neutrino-induced charm. By reanalyzing E531 data, combining updated charm-hadron fractions with refined branching ratios, and employing ratio observables that minimize systematics, the study yields a direct |V_{cd}| value of 0.232 with about 9% total uncertainty, consistent with CKM unitarity. The paper also benchmarks current constraints against indirect measurements and outlines future experiments (Nomad, Chorus, NuTeV, COSMOS, TOSCA) that could achieve precision competitive with or surpassing |V_{us}|, thereby providing a stringent test of the CKM framework and potential new physics if deviations emerge.

Abstract

The formalism for extracting the CKM parameter $V_{cd}$ from $νN$ production of charm is discussed in some detail. The various model assumptions needed are clearly pointed out. A direct determination from neutrino induced dimuon production requires $νN$ charm production data, $% νN$ charm hadronization data, and the semi-muonic branching ratios for charmed hadrons. Hadronization data from FNAL E531 is re-analyzed to take advantage of better-determined properties of the charmed hadrons. A small bias in the original published result is removed. Neutrino induced charm fragmentation is compared to $e^{+}e^{-}$ charm fragmentation functions; the data are consistent with a common hadronization scheme. An updated value of the mean semi-muonic branching ratio for charmed hadrons produced in $νN$ scattering for $E_ν>30$ GeV is obtained. This value is used to determine $% V_{cd}$ and its associated uncertainties. Prospects for improving the $% V_{cd} $ measurement to test the unitarity limit of the CKM matrix are described.